Théorie

Probing scalar-tensor theories with compact binaries

Until now, observations and experiments have confirmed General Relativity (GR) as the best theory of gravity. The current gravitational wave interferometers, LIGO and Virgo, as well as the future space-based detector LISA, will permit to challenge further GR in the highly dynamical and strong field regime of gravity. In this talk, I will focus on alternative theories with an additional scalar degree of freedom, in relation to compact objects.

Primordial black holes and the inflationary universe

The interest in primordial black holes (PBHs) has recently risen up 
again after the discovery of around 30 solar mass black holes through 
the LIGO/Virgo gravitational wave events. PBHs are black holes produced 
by gravitational collapse of the over-dense region in the early universe.
 An attractive origin of the overdensity is primordial perturbations 
generated during inflation. In this talk, I will first explain the 
relation between the power spectrum of the perturbations predicted by 

Transport effects due to quantum anomalies

Anomalous transport phenomena emerge in systems where quantum anomalies break certain classical symmetries leading to nonconservation of associated, and otherwise classically conserved, currents. In backgrounds of magnetic or gravitational fields, as well as in rotating systems, the anomalies may generate nondissipative flows of energy and charge currents even in the presence of strong interactions. We review recent theoretical developments on the anomalous transport in systems possessing axial, axial-gravitational, and conformal anomalies.

Hamiltonian vs stability in alternative theories of gravity

When a Hamiltonian density is bounded by below, we know that
the lowest-energy state must be stable. One is often tempted
to reverse the theorem and therefore believe that an unbounded
Hamiltonian density always implies an instability. The main
purpose of this talk is to pedagogically explain why this is
erroneous. Stability is indeed a coordinate-independent property,
whereas the Hamiltonian density does depend on the choice of
coordinates. In alternative theories of gravity, like k-essence
or Horndeski theories, the correct stability criterion is

Carrollian fluids and flat holography

Various extensions of the AdS/CFT correspondence beyond the realm of asymptotically anti-de Sitter spacetimes have been proposed. Among those, the asymptotically flat spacetimes have played a distinguished and recently revived role. With the exception of three spacetime dimensions, and despite the wide interest and the precise knowledge of the asymptotic symmetries, no concrete proposal was available.

Stochastic inflation, primordial black holes, and beyond the slow-roll approximation

I will explain how primordial black holes can form from
perturbations seeded during inflation and how their abundance can be
calculated in the framework of stochastic inflation. This formalism
incorporates quantum backreaction of the small-wavelength fluctuations
on the large distances dynamics of the Universe. If quantum
corrections are small, the probability distribution of density
fluctuations is well approximated by a Gaussian. If they are large,
the PDF has a different profile with a longer tail and leads to

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